METABOLISM, AND EXCRETION
Both atropine and scopolamine
are tertiary amines that cross biological membranes readily. They are well
ab-sorbed from the gastrointestinal tract and conjunctiva and can cross the
blood-brain barrier. After the intra-venous injection of atropine (DL-hyoscyamine), the
bio-logically inactive isomer, D-hyoscyamine, is excreted un-changed in the urine. The active
isomer, however, can undergo dealkylation, oxidation, and hydrolysis.
The quaternary ammonium
derivatives of the bel-ladonna alkaloids, as well as the synthetic quaternary
ammonium compounds, are incompletely absorbed from the gastrointestinal tract.
Consequently, greater amounts of these compounds are eliminated in the feces
following oral administration. The blood-brain barrier prevents quaternary
ammonium muscarinic blockers from gaining significant access to the CNS.